Foil insulation - observations, tips and tricks

[malconium]

I was finally able to spend several hours today finishing the installation of reflective foil insulation in the walls of my 1973 31' unit. I am now ready to start re-installing the rest of the skins. Actually I have already re-installed the skins and end caps at both ends of the trailer. At any rate I thought that it would be a good time to pass on some observations that I have made along the way and to offer some suggestions to other who want to install reflective foil.

The main target of the installation was to fill each part of the wall cavity with reflective foil insulation in such a way as to keep an air gap on each side of the foil as much as possible. Foil insulation works more effectively if there can be an air gap on each side. So I bought some sheets of 1/2" and 1" thick styrofoam insulation board that I cut into 1" wide strips on my table saw. I had wanted 3/4" thick panels but for some reason that thickness was not availabe at Lowes or Home Depot at the time. Of course not it is.

I glued strips of the foam around the edges of each cavity and sometimes in the middle of larger cavities or ones that were especially curved. Initially I was installing the 1" strips first, glueing the foil to the 1" strips and then adding 1/2" strips on top of the foil in the same places where I put the 1" strips. Since the foil does have some thickness this means that the foam will have to compress a bit when I put my skins back in. This was not a problem when I installed the skins at the ends of my unit.

Somewhere along the line in one of the discussions that we have had here on the forums about foil insulation someone (I am sorry but I don't remember who) suggested that they were going to just glue the foam to the outer skin and glue the foil to it. There idea was to make sure and use glue that stuck well enough that the inner strips were not needed. I have since decided that this approach makes a lot of sense. So that is the approach that I have taken for about the last 40% of my installation.

So here is what I suggest as a good approach based on the experimenting that I did during my own installation:

1.) Use 1/2" or 3/4" foam cut into strips about 1" wide. Lowes has started carrying the foam board in 2' x 4' pieces which are much easier to handle than the 4' x 8' pieces I started with. The funny thing is that 4 - 2' x 4' sheets of 1/2" foam was actually a little cheaper than a 4' x 8' sheet when I bought the last of my foam. You can also cut it as you need it and return any unused sheets if you over estimate.

2.) Pick glue that sticks well to metal. I started using Liquid Nails which did seem to work OK but when I needed more I found another product at Lowes that was about 1/2 the price and works at least as well. The produc name is "Nail Power". It says that it is recommended for gluing drywall to wood and metal studs. I think I paid less than $1.50 per tube for it. It is kind of smelly though so make sure you have good ventilation. Liquid nails is not as smelly but I think I paid over $3 per tube and it does not seem to work any better.

3.) Just put strips on the outside skin and glue the foil to it. At first I tired to put the foam strips as tight to the sides of each cavity as possible. That is a little hard since some of the framing bulges here and there. I finally concluded that it was better to go for nice flat areas even if they were an inch or so inboard of the cavity edges. The foam is there to holf the foil away from the outer and inner skins. As long as it does that all is OK.

4.) There are some really odd shaped pieces of foil that have to be cut to fit around things like windows and etc. At first I tried holding a piece of foil up against the wall and used a razor knife to cut around the window frame. Right neart the end of my installation I found a much better approach. It turns out that if you hold the foil in the place where you want it that you can press the foil down around the edges of the obstacle. The back side of the foil now has a very nice line pressed into it that you can easily follow with scissors.

5.) I also discovered (late) that I could cut larger pieces for more than one cavity and mark as above. I cut then slit the foil so that it would clear things like cross members in the cavities.

I hope some of these ideas help. I would be happy to answer any questions that anyone has. I could also add some photos if it is not obvious enough what I am talking about. Also feel free to chime in with good ideas that you have discovered doing the same thing.

Malcolm

[john hd]

malcom

i was wondering how your project was coming along. does the trailer seem to hold heat well? any impressions on that yet?

the insulation is good stuff, i use it in my chicken coop. seems to work well except the biddies get bored and peck at it!

john

[Jim & Susan]

Thansk for the tips Mal. I've tried construction adhesive to attach things to the outer skin with poor results. Just today, I tried using Vulkem. I'll let you know in a few days how it turned out.

Jim

[SmokelessJoe]

Malcom, Jim, John, others:

A purpose made glue for this application is PL 300 Foam Adhesive


http://www.stickwithpl.com/Products....Board-Adhesive


Sergei

[packdad52]

While researching insulation for my attic I ran across a company that sells closed cell polyurethane spray foam in cans that look like gas grill bottles. The material is measured in board feet 12"x12"x1" and cost about a dollar a board foot. Has anyone ever used this on an airstream and if so with what results. I was just curious.

[boatdoc]

Hi Malcom; Thank you for sharing your experience of insulating your trailer.
I am about to do the same on my 1973 26' Argossy. As you most likely know we have built a new SS frame with 1/2" aluminum skinned plywood floor, which was joined with aluminum H molding and C trim around all edges with 3M 5200 sealing each joint. The underside of the floor I have glued 1" x 2" urethane foam strips as shown in my posted pics. Bubble foil was glued onto the strips and edges were sealed with 5200. All inner skins were stripped except the end caps. The rear end cap has a couple of large cracks which will be repaired from the back with Vinyl ester Resin and Kevlar cloth. I have all wiring in place however, 12 volt DC system was changed. On street side rear where the hot water heater access door was, a SS rubber lined sealed housing will be installed for two Group 29 Deep cycle batteries. Hot water heater will go on opposite side where unused access door is located just ahead of shower tub. 6 gage wires will power up a panel located inside the front end cap. This circuit will serve overhead lights and monitors as well as the fans, stove,ceiling, outside light and sound system. The rear panel above the batteries in a linen closet will handle the rest of circuits. Returning to the insulation I have one recommendation. I am going to form the foil along the ribs all the way to the inner skins in order to reduce heat transfer through the ribs. At my local lumber yard I have purchased 1/2" urethane foam for spacers. Home Depot nor Lowe's had it. My wiring will be on the inner skin side, in a event that there is a need to service it. All edges will be sealed with #5200. I am concerned about finishing it before the summer and my head hurts from amount of work to be done yet as I am entering my busy time in my boat business. Thanks for sharing your ideas. "Boatdoc"

[tinbender]

Malcom,

Great detailed info and timely for me. I am working on some like projects. The one question I have is, how did you deal with the wheel wells? I have just finished repairing my inside covers and I don't want to simply replace the pink fiberglass if there is a better option.

Thanks again for really useable info.

TinB

[SmokelessJoe]

Tin B

You can insulate between the outer and inner wheel well covers as shown here:







Sergei

[malconium]

Originally Posted by SmokelessJoe

Malcom, Jim, John, others:

A purpose made glue for this application is PL 300 Foam Adhesive


StickWithPL - Sealants, Adhesives Products Page


Sergei

This does sound like a good product for the purpose. Is it commonly available at places like Lowes or Home Depot? About what does it cost per tube?

Thanks for the input,

Malcolm

[malconium]

I have not actually installed my inner wheel wells yet. I have to put the inner skins back on first. SmokelessJoes approach looks fine as one approach. What I had in mind was to use the foil insulationt there too. I was thinking about glueing the foam strips and foil on top of the outer wheel well and then putting the inner one back in place.

I have also wondered if I should just box in the wheel wells as part of my cabinet building. Both of the wheel wells will potentially be inside of cabinets or along the edge of the bathroom. My floor plan was side bath. I have a brand new set of inner wheel wells that I would want to sell if I took that approach. Has anyone done it that way?

Malcolm

[malconium]

Originally Posted by boatdoc

Hi Malcom; Thank you for sharing your experience of insulating your trailer.
I am about to do the same on my 1973 26' Argossy. As you most likely know we have built a new SS frame with 1/2" aluminum skinned plywood floor, which was joined with aluminum H molding and C trim around all edges with 3M 5200 sealing each joint. The underside of the floor I have glued 1" x 2" urethane foam strips as shown in my posted pics. Bubble foil was glued onto the strips and edges were sealed with 5200. All inner skins were stripped except the end caps. The rear end cap has a couple of large cracks which will be repaired from the back with Vinyl ester Resin and Kevlar cloth. I have all wiring in place however, 12 volt DC system was changed. On street side rear where the hot water heater access door was, a SS rubber lined sealed housing will be installed for two Group 29 Deep cycle batteries. Hot water heater will go on opposite side where unused access door is located just ahead of shower tub. 6 gage wires will power up a panel located inside the front end cap. This circuit will serve overhead lights and monitors as well as the fans, stove,ceiling, outside light and sound system. The rear panel above the batteries in a linen closet will handle the rest of circuits. Returning to the insulation I have one recommendation. I am going to form the foil along the ribs all the way to the inner skins in order to reduce heat transfer through the ribs. At my local lumber yard I have purchased 1/2" urethane foam for spacers. Home Depot nor Lowe's had it. My wiring will be on the inner skin side, in a event that there is a need to service it. All edges will be sealed with #5200. I am concerned about finishing it before the summer and my head hurts from amount of work to be done yet as I am entering my busy time in my boat business. Thanks for sharing your ideas. "Boatdoc"

Boatdoc,

It sounds like you are going to have a really spectacluar end product! Some of what you are doing sounds like overkill to me - I don't have the patience that you evidently do. You will certainly have a great trailer when you are done though.

I did not know that urethane foam board was available. Lowes and Home Depot ceratainly don't carry it. Does the product you bought have a brand name? Is it available in other thicknesses? Urethane foam has a much higher insulation R value per inch than styrofoam does. As I recall it is about R7 per inch compared to about R 3 or 4 per inch of styrofoam.

Where do you get the 3M 5200? Is it a caulk or is it also a glue?

Malcolm

[malconium]

Originally Posted by packdad52

While researching insulation for my attic I ran across a company that sells closed cell polyurethane spray foam in cans that look like gas grill bottles. The material is measured in board feet 12"x12"x1" and cost about a dollar a board foot. Has anyone ever used this on an airstream and if so with what results. I was just curious.

There has been some discussion here on the forums from time to time about using spray in place foam insulation. You can probably find the postings if you search for "foam". I remember reading that some people have used it under the floor. I don't recall anyone having used in their walls but someone may have.

Generally the sentiment seems to be that it is not the best thing to use. Some people have said that it will eventually disintegrate because of road vibration. I am not sure that would be a big problem if the insulation is contained and does not lose its R value if it is in pieces. The other problem is that it would fully encapsulate wiring and other things making it very hard to fix something if you had to later. It would be pretty expensive too. The wall cavities are about 1-1/2" to 1-3/4" deep which means that you would need at least 1.5 board feet per square feet of wall. On my 31' Airstream I have somewhere in the range of 400 to 500 square feet of walls. That means that the spray in place foam could run up to about $700 or $800 dollars for the walls. I also have about 200 square feet of floor so that would add even more. The reflecive foil insulation sells at Home Depot and Lowes for less than 50 cents per square foot. I belive it is available other places for even less if you shop around the Internet. That means that the foam approach would be more than three times the cost of foil.

On the other hand I do know that new high-end trailers of other brands are using square aluminum tubing and fiberglass foam-core wall construction. Sine the fome in that type of insulation is part of the structure they must have picked a type of foam that will not disitegrate with road vibration.

Malcolm

[malconium]

I forgot to mention some observations that I made about the wiring. In my unit virtually all of the original wiring is intact and will probably end up being used. One thing that I noticed while installing my foil was that I was not entirely sure exactly where each wire was going to come through the inner skin. My inner skins are all staked in the garage and not convenient to get to to take measurements while installing the foil. So what I ended up doing was to keep most of the wiring on the inside of the foil so that it would be easier to fine tune its route when I put the skins back in place. The main exception to this is that I ran some parts of the 110 volt wiring against the outer skin until I got closer to where the outlets would be. That made it a bit easier to secure the wires which are a bit heavy. I used glue on tie down anchor squares and plastic tie straps. Lately I have been ignoring the glue on the square and adding some of the panel adhesive I have been using.

My AS was mostly gutted inside when I got it. I know that all the 110 volt outlets work and I have used them for power tools or lights during my construction on the trailer. What I didn't think to do before I took everything about was to carefully check all of the 12 volt wiring before I disassembled everthing. I did at least put labels on all of the wires. I think that I will need to test the wires before I put my skins back on. It would have been easier to test everything will the fuse panel was still hooked up and most the lights and etc. were still in place. Now the fuse panel is out and nothing is connected at the ends of the wires. I will need to rig up a test curcuit using my battery and some alegator clips or some such thing.

Now I am going to have to give carefull consideration to my floor plan before I put the skins back in place. It would be much easier to add new wires now rather than after I put the skins back in place.

Malcolm

[malconium]

Another thing that I forgot to mention here is a note about how I intend to insulate my floors. I like the approach that Boatdoc is taking with the foil under the floor and would use that technique myself except for three reasons.

The first is that I have not actually removed all of my belly pan and don't intend to if I can avoid it. The belly pan for the front half of the trailer is in really good shape and I did not want to have to remove it. I also was able to replace my floor from above in those areas. I used a product called Polyboard by the way. If anyone is interested in checking that out do a search by that keyword and I think you will find postings about what I did.

The second reason is that a lot of my underfloor space will have holding tanks of various types in them. The fresh water tank on a 1973 31' unit takes two of the floor cavities under the kitchen area. I intend to add a combination black and grey tank in another cavity just behind the rear axels. If I don't go with the combo tank I would put a black water tank in another cavity. These tanks are a bit in the way of underfloor insulation technique. Yeh, I know that I need to provide some insulation for my tanks too and that would help.

The other reason is that I am still thinking about putting hot water radiant heating on top of my floor. If I do indeed take that approach what I was intending to do was to put down a layer of reflective foil on top of the floor and put PEX radiant heat tubing on top of that. It is not as good of a solution overall as putting the foil under the floor but I thought it would serve my needs OK. It should work pretty well to prevent heat loss and not quite so well to prevent heat gain in hot weather. the extra air gap because of the radiant heating will help some though. I still have to decide what type of flooring to put on top of the radiant heating. I do have about 200 square feet of some 3/8" thick tounge and groove brazillian koa wood flooring left over from another project that would look awesome. It would not be as durable as something like laminate flooring though. Also the koa wood needs to be or glued down and I would prefer something that floated. We shall see about that one...

Malcolm

[SmokelessJoe]

Malcolm:

PL 300 is made by HENKEL, a very large chemical company out of Ohio.

It's sold at every HOME DEPOT store (and everywhere else) in Canada so it should be available at your big box stores too.

About $4 or $5 a caulking-gun tube.

Contractors use it to glue all types of foam board to pretty wel anything.

I used it while insulating the trailer.

I don't know why I didn't add a layer of bubble foil to the wheel wells. I have lots of it left over from insulating the walls.

Maybe I'll lift the top off and add a layer. It's only a few screws and rivets.


Sergei

[boatdoc]

Hi Malcom; 3M 5200 is available in any boat store. It is a permanent adhesive sealant. It is watertight bonds just about to anything. Fast Cure cures in 24 hours. It is a one part polyurethane but it is not recommended for bonding windows. Try 3M Marine Products. Thanks "Boatdoc".

[tphan]

hi all- interesting thread, I have to do something along these lines next summer. Tell me again please, what are the drawbacks to completely covering the underside of the plywood with foam sheets- filling the entire space between the ribs/joists? And then covering that with foil-bubble, both for added r-value, and protection/containment of the foam? Just thinking out loud here, wanting the best durable r-value as a lot of cold seems to come from the floor. Does the foam NOT create the desireable air-space for the foil? Thanks- tim

[Jim & Susan]

Malcolm, I traced all of the wire in the camper and posted it in my Full Monty thread, in case you need it. I suspect that my 27' and your 31' use the same wiring bundle: http://www.airforums.com/forum...7-post360.html

Jim

[malconium]

Originally Posted by tphan

hi all- interesting thread, I have to do something along these lines next summer. Tell me again please, what are the drawbacks to completely covering the underside of the plywood with foam sheets- filling the entire space between the ribs/joists? And then covering that with foil-bubble, both for added r-value, and protection/containment of the foam? Just thinking out loud here, wanting the best durable r-value as a lot of cold seems to come from the floor. Does the foam NOT create the desireable air-space for the foil? Thanks- tim

I think that an air gap next to the foil is what helps the foil do the best job. Foam right next to the foil might not be as good as air next to the foil as far as blocking the flow of radiant energy. It is also my belief that if you put a layer of foil below the bottom of your floor by an inch or two that you don't really need the foam too. For that matter it seems to me that you could use the foam by itself and not really need the foil. The foam board that I have seem at Home Depot and Lowes has a plastic vapor barrier on it that might be enough protection. I have also seen some polyisocyanurate foam (at Home Depot I think) That has a foil skin on it.

Personally I would put just the foil under the floor and figure out some way to suspend it a bit below the bottom of the floor such as suggested above using something like strips of foam around the edges of each cavity.

Malcolm

[malconium]

Originally Posted by Jim & Susan

Malcolm, I traced all of the wire in the camper and posted it in my Full Monty thread, in case you need it. I suspect that my 27' and your 31' use the same wiring bundle: http://www.airforums.com/forum...7-post360.html

Jim

Thanks for the tip. It does look like it might be different than mine, though, at least some. I see in my service manual that the 27 wiring schematic is about the same as a rear bath 31'. Mine is a side bath 31'. Is your 27' indeed a rear bath model?

Thanks,

Malcolm